MQTT.js 订阅从代理接收多个相同消息答案

【问题标题】：MQTT.js subscription receives multiples of the same message from the brokerMQTT.js 订阅从代理接收多个相同消息
【发布时间】：2017-09-07 23:37:56
【问题描述】：

我在 CloudMQTT 上运行，我的 JS 代码是这样的：

var mqtt_url = URL.parse('mqtt://m10.cloudmqtt.com:15272' || 'mqtt://localhost:1883');
var auth = (mqtt_url.auth || ':').split(':');
var url = "mqtt://" + mqtt_url.host;

var options = {
  port: mqtt_url.port,
  clientId: 'mqttjs_' + Math.random().toString(16).substr(2, 8),
  username: USERNAME,
  password: PASSWORD,
};

// Create a client connection
var client = mqtt.connect(url, options);

client.on('connect', function() { // When connected

  // subscribe to a topic
  client.subscribe('relay', function() {
    // when a message arrives, do something with it
    client.on('message', function(topic, message, packet) {
        // console.log(packet);
      console.log("Received '" + message + "' on '" + topic + "'");
    });
  });

  // subscribe to a topic
  client.subscribe('photoresistor', function() {
    // when a message arrives, do something with it
    client.on('message', function(topic, message, packet) {
      console.log("Received '" + message + "' on '" + topic + "'");
    });
  });

  // publish a message to a topic
  client.publish('relay', value, function() {
    console.log("Message of ", value, " is published");
    // client.end(); // Close the connection when published
  });

});

我将我的ESP8266 连接到一个光敏电阻，它每 5 秒将光敏电阻值发布到 photoresistor 主题一次。

好吧，我每隔 5 秒就会在我的 Node 服务器 (MeteorJS) 上获得四个相同的控制台日志。

I20170907-19:33:51.421(-4)? Received '156' on 'photoresistor'
I20170907-19:33:51.423(-4)? Received '156' on 'photoresistor'
I20170907-19:33:51.424(-4)? Received '156' on 'photoresistor'
I20170907-19:33:51.425(-4)? Received '156' on 'photoresistor'
I20170907-19:33:57.741(-4)? Received '39' on 'photoresistor'
I20170907-19:33:57.742(-4)? Received '39' on 'photoresistor'
I20170907-19:33:57.743(-4)? Received '39' on 'photoresistor'
I20170907-19:33:57.743(-4)? Received '39' on 'photoresistor'
I20170907-19:34:05.465(-4)? Received '37' on 'photoresistor'
I20170907-19:34:05.467(-4)? Received '37' on 'photoresistor'
I20170907-19:34:05.468(-4)? Received '37' on 'photoresistor'
I20170907-19:34:05.470(-4)? Received '37' on 'photoresistor'
I20170907-19:34:10.665(-4)? Received '161' on 'photoresistor'
I20170907-19:34:10.667(-4)? Received '161' on 'photoresistor'
I20170907-19:34:10.667(-4)? Received '161' on 'photoresistor'
I20170907-19:34:10.668(-4)? Received '161' on 'photoresistor'

知道什么可能导致client.subscribe 函数或 CloudMQTT 输出多个相同消息吗？

【问题讨论】：

您是否检查过其他客户端（例如 mosquitto_sub）是否有多个消息正在发布？
你有没有弄明白这个？我看到了完全相同的问题。有什么想法吗？

标签： javascript node.js mqtt esp8266

【解决方案1】：

似乎在某些情况下，在连接事件处理程序中订阅可能会导致重复订阅。如here 所述，mqtt.js release 2.9.0 解决了这种性质的问题。因此，升级到最新的 mqtt.js 版本（当前为 2.13.1）可能会解决您的问题。

但是，还要注意mqtt.js usage notes 声明“从 v2.0.0 开始，如果 clean: true 则在重新连接时恢复订阅”。另见here。如果是这样，您似乎根本不需要在连接事件处理程序中进行订阅，这应该有望从一开始就防止重复订阅发生。

您应该可以很简单地在连接 node.js 客户端时重新启动 CloudMQTT 代理来测试上述假设。这是否会导致您开始看到重复的消息？如果是这样，我相信补救措施确实是将您的订阅移动到连接事件处理程序之外。

【讨论】：